This invention relates to powder metallurgy and more particulary to the consolidation of metal powders into hollow, cored, and composite shaped parts of nearly solid metals.
Hundreds of thousands of straight tubular fittings made of the Nitinol class of shape change alloys have been used in pressurized and unpressurized pipe and tubing systems in ships and aircraft. These fittings can be connected without expensive welding procedures. However, straight tubular fittings make up only a small fraction of the tubular fittings in these systems. Considerably greater savings can be realized if the more complex fittings, such as tees, ells, crosses, and wyes, can be economically made of the Nitinol alloys.
Unfortunately, these complex fittings can not be cast from Nitinol alloys and machining such shapes from solid Nitinol metal alloy is prohibitively expensive. Nor can state of the art powder metallurgy techniques be used to produce these complex fittings from the Nitinol alloys. The "hot isostatic pressing" (HIP) process requires that the alloy powder be sealed in expensive welded metal cans of the desired shape and placed in special, very expensive chambers capable of applying high temperature and pressure at the same time. Even for simple forms this is an extremely expensive procedure. Another common procedure is called the CIP-sinter process in which the alloy powders are compacted at ambient temperature and then vacuum sintered. This procedure is unsuitable for producing complex fittings of sufficient density.
U.S. Pat. No. 4,227,927 which issued to Herbert L. Block and Jerome Schwertz on Oct. 14, 1980, discloses the CAP.RTM. process, "consolidation by atmosphere presure". In this process the metal powder is enclosed within an evacuated glass container, which is then embedded within a free flowing refractory powder, such as graphite, and heated within an air atmosphere furnace. This process, however, has been limited to producing solid objects such as in the tool industry. In order to produce pipes and other hollow objects double walled glass molds would be required. Such molds for complex fittings such as tees, crosses, wyes, etc., would require highly skilled glass blowers and would be prohibitively expensive.
It therefore would be desirable to provide a relatively inexpensive process for producing complex-shaped fittings of Nitinol alloys which have high density and strength.